1. Technical Field
The present invention relates to plasma etching apparatuses. More specifically, the invention relates to a plasma etching apparatus including an electrode for generating plasma of a reactant gas in a chamber by inductive coupling or by inductive coupling and capacitive coupling via a high-withstand-pressure dielectric member so as to fulfill etching.
2. Background Art
Such plasma etching apparatuses are already known (see, e.g., Patent Literatures 1 to 3).
An apparatus disclosed in Patent Literature 1 includes a metallic beam or frame body with a plurality of through windows formed therein, and a dielectric supported by the frame body to seal the chamber. Patent Literature 1 teaches as follows. With this construction, the dielectric can be reduced in thickness to thereby reduce dielectric loss, while enough pressure strength can be secured by support using a metallic beam or frame body. As a result, it becomes possible to generate high-density plasma over a large area under high vacuum by inductive coupling from the coil or the like. Thus, low-priced plasma processing excellent in durability and electrical efficiency of applied power is realized.
The apparatus disclosed in Patent Literature 2 includes a dielectric member of honeycomb construction in which a plate-shaped portion and a single beam or plurality of beams are integrated together. This dielectric member is placed directly on an upper opening of the chamber without intervention of the frame body. Patent Literature 2 teaches that enough planar strength can be secured by the dielectric member itself by virtue of the honeycomb construction while loss or interception of radio frequency waves from the coil can be solved by eliminating the metallic frame body.
The apparatus disclosed in Patent Literature 3 includes a top plate which is made from a dielectric and in which a recess portion is formed in at least one of its chamber-side surface and its counter-side surface. A thickness of the top plate in this recess portion is smaller than a thickness of the top plate in the other portion. More specifically, the thickness of the top plate in the recess portion is set to one half or less of a wavelength at which the radio frequency wave propagates through the top plate. Patent Literature 3 teaches as follows. The top plate is enabled to secure enough mechanical strength by its having a thicker portion as well as a thin portion. Also, while a radio frequency wave passes through the recess portion, its components directed sideways are reflected by a side wall of the recess portion, thus making the downward directivity intensified. When the recess portion is formed in the surface counter to the chamber, the plasma generation surface is not kept away from an object to be treated so that the directivity can be enhanced. As a result of directivity enhancement, plasma or radicals in vicinities of the object are improved in terms of density.    Patent Literature 1: JP H10-27782 A    Patent Literature 2: JP 2000-200698 A    Patent Literature 3: JP 2004-14262 A
The apparatus disclosed in Patent Literature 1 necessitates a beam or frame body other than the dielectric, thus being complex in structure and high-priced in component manufacture and assembling costs. Also, the metallic beam or frame body is located near a plasma generation site so as to be exposed to high-density plasma. The beam, which is made of such a metal as aluminum or stainless steel, is liable particularly to occurrence of metal contaminations. Furthermore, if reaction products generated by plasma etching are deposited onto the beam or frame body during mass production of wafers, the presence of recesses and protrusions formed by the beam or frame body on the chamber inner wall side causes the deposited reaction products to be more likely peeled off, making particles generated, so that the maintenance cycle becomes shorter.
The apparatuses disclosed in Patent Literatures 2 and 3 are generally common to each other in that the mechanical strength is secured by a simple beam structure in which a thin portion and a thick portion of the dielectric are integrally formed, and that the thin portion provided in the dielectric allows radio frequency waves or the like to pass therethrough. The apparatus disclosed in Patent Literature 2 adopts a construction that a coil turned and expanded from a center to peripheries passes through all grid-like beams. This construction allows the whole coil to be placed at a lower position, i.e., closer to a lower surface of the dielectric without influences of the beams. Accordingly, the apparatus is advantageous for loss or interception of radio frequency waves with respect to any portion of the coil, but structure and assembly of the apparatus are complex and expensive.
On the other hand, a semiconductor wafer, which is a treated object of plasma processing, has been increasing in diameter more and more, as large as 200 mm to 300 mm at the present time, while the chamber for treating the wafer has been further increasing in inner diameter, as large as 320 mm to 450 mm. Still more, etching has been attaining higher precision while the etching depth has also been increasing. In order to meet these requirements, there is a need for generating plasma more uniformly and more vigorously over a wide area.
Another problem that matters in some cases is increases in deposition amount of reaction products onto the lower surface of the high-withstand-pressure dielectric member. In particular, in plasma etching of a nonvolatile material, since reaction products and/or nonvolatile materials of sputtering or the like are deposited on the high-withstand-pressure dielectric member, the radio frequency induction electric field or inductive coupling power from the coil is subjected to degradation of transmissivity and/or disturbing of transmission places, causing decreases in plasma density or decreases in plasma uniformity. In contrast to this, in the case where an electrode for capacitive coupling is placed between the high-withstand-pressure dielectric member and the coil in terms of removal or deposition prevention of reaction products, this electrode incurs loss or interception of a radio frequency wave transmitted from the coil through the high-withstand-pressure dielectric member into the chamber, causing a need for avoiding this occurrence.
However, although the apparatus disclosed in Patent Literature 3 has a chamber-sealed structure of low cost and high durability using a high-withstand-pressure dielectric member alone, a construction that allows uniform, vigorous plasma to be generated over a wide area cannot be realized even in combination with the disclosures of Patent Literatures 1, 2. What is more, it is impossible to realize generation of uniform, vigorous plasma over a wide area while the capacitive coupling action from the electrode is utilized for deposition prevention or removal of reaction products.